The present invention relates to a gas/liquid contact tray for use in a column for counter-currently contacting gas and liquid. Such a column is any column in which gas and liquid are counter-currently contacted to exchange heat or matter. An example of such a column is a fractionation column and a further example is a vacuum distillation column.
In such a column liquid flows, during normal operation, downwards from top to bottom, whereas gas flows upwards from bottom to top. In the specification and in the claims the word xe2x80x98gasxe2x80x99 is used to refer to gas and to vapour.
Such a column is provided with a number of horizontal gas/liquid contact trays arranged one above the other. Each tray comprises a perforated panel provided with one or more downcomers. The downcomer is a conduit for downward passing of liquid arranged in an opening in the perforated panel, the part of the wall of the downcomer extending above the perforated panel is called the downcomer weir, and the part of the downcomer extending below the perforated panel is called the downcomer apron.
During normal operation liquid collected on a tray flows over the perforated panel where it is contacted with upwardly flowing gas passing through the perforations. Then the liquid will flow over the downcomer weir into the downcomer and onto the perforated panel of the tray below, and so on. It will be understood that the downcomers of two adjacent trays are not placed directly above each other, but spaced apart in lateral direction (or staggered) in order to prevent liquid from falling directly into the downcomer of the lower tray. Moreover, the downcomers are so located that the liquid exiting the downcomers can flow evenly over the perforated panel. In this way it is achieved that the time during which gas and liquid are in contact with each other is independent from the position of a liquid element on the perforated panel.
The gas/liquid contacting tray to which the present invention relates comprises a perforated panel of which the area is divided in two or more parallel sections, wherein either the odd numbered sections or the even numbered sections are provided with a plurality of downcomers directed perpendicular to the direction of the section, and wherein the bottoms of the downcomers are provided with lateral outflow openings directed in the direction of the sections.
Such a gas/liquid contacting tray is disclosed in Belgian patent specification No. 584 426, and described in more detail with reference to FIGS. 8, 9 and 14 IV.
The gas/liquid contacting tray shown in FIGS. 8 and 9 of this publication comprises a perforated panel of which the area is divided in two parallel sections, wherein either the first section (FIG. 8) or the second section (FIG. 9) is provided with a plurality of downcomers directed perpendicular to the direction of the section, and wherein the bottoms of the downcomers are provided with lateral outflow openings directed in the direction of the sections. This arrangement is selected to get an even distribution of liquid flowing during normal operation over the perforated panel, so as to prevent a stagnant zone near the edge of the perforated panel, where the liquid could reside longer than the average residence time of liquid on the tray. Applicant, however, had found that this arrangement did not fully eliminate the stagnant zone.
It is an object of the present invention to overcome this problem.
To this end the gas/liquid contact tray according to the present invention for use in a column for counters-currently contacting gas and liquid comprises a perforated panel of which the area is divided in two or more parallel sections, wherein either the odd numbered sections or the even numbered sections are provided with a plurality of downcomers directed perpendicular to the direction of the section, wherein the bottoms of the downcomers are provided with lateral outflow openings directed in the direction of the sections, and wherein the bottom of each downcomer in the section(s) neighbouring the wall of the column is also provided with a frontal outflow opening directed in the direction of the wall.